From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 39AF63E40E0; Wed, 30 Sep 2026 09:48:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790761740; cv=none; b=nACAPDWSGi5otTnuUL5JeJhva44TC+xeMBsETZqpUbqhAa0QS3fcwKQIIkP/W30OehBYywYrRcbgSJ58mmXuehon5A7Lg5S7Dz/UnkfsLjBmfQANM+ME6FEDx7yfc9cbu6P3vI2+5cKcUpUPxmNP2oHw+aSU4hqGzyX/Y83AXjk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790761740; c=relaxed/simple; bh=SsJFafcydfK+cId6DIHrbXEjx31Yrp/pBnHbcQfg+/M=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oqv0aqHQ25ucs6any7uU51Qk4P37KcCNQSiNB+K+fZgJ9o7vfhXMCP9Kxw/laRaxmngFN/RwAi8ixYDgjmaV4IGQJ8dlxGUsQX3rjB24cv64mvnRFcfhMC6hYtOgqYoRVHn/kJBhVlWPW0eYGY0/hk34hhxu1suFrFAFgEtF+tE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ALC3ltrK; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ALC3ltrK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5563C1F000FF; Wed, 30 Sep 2026 09:48:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790761738; bh=Nl9MeDTY24eQyQhffUb7xAuQNY3nKyWvog2voZwmldo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ALC3ltrKN3qos9OvyQMmGJkaw+ZmlpnFqbIdT1bYSF3Cb5SJESDXXkiJpZNOigxtI MoChgdvVQXgz6EthkGaeKysgMiPi7P+vU6bCU13PtDm4k4Fi+OV5GtnB1fcXybGEHP 1PV2wiGf8yhhMkQm2UJNk6izPP7tsx9qvJSnxhWyq/xbGmC0MUHcad8P+EywX+gt1j 6Hcn8c5VHWs3n0fhsWgUI+FImoPxGsnCyJ+QhRMCL41kkiazG2FzwpsYBmRDLR2+EB dVXFx5Bz8oWYwJD2C9kXtUkouL6qXsoMc6U62XO+7b6Tr2lzsdrYVmmn7LCqIh22Sz uj9OguUgr3+Lg== From: SJ Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, Liew Rui Yan , SJ Park , Andrew Morton Subject: [PATCH 6.1.y] mm/damon/core: fix unconditionally skip last region Date: Wed, 30 Sep 2026 02:48:53 -0700 Message-ID: <20260930094853.52736-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026092949-surpass-thimble-02a8@gregkh> References: <2026092949-surpass-thimble-02a8@gregkh> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Liew Rui Yan Once quota set, the charge_{target,addr}_from unconditionally skips and resets at the last region of the tracked target, so the last region can be skipped even when it has not been processed. Example: 1. Target has 2 regions: R1 (0-100 bytes) and R2 (100-200 bytes). 2. Quota is configured to process only 100 bytes per window. 3. Window 1: Processes R1 (0-100). Quota is full. charge_{target, addr}_from is saved at (Target, 100). 4. Window 2: The loop reaches R2. Because R2 is damon_last_region(t), the old code unconditionally returns true, skipping R2 entirely and resetting the charge_{target,addr}_from. Result: R2 is permanently skipped even though it has never been processed. However, it is important to note that this is a very minor issue. This is because it is triggered only when the previous window saved/kept charge_{target,addr}_from, and in the next window, all regions except the last region were skipped by damos_skip_charged_region(). Fix this by only resetting the charge_{target,addr}_from when last region is reached, only skipping when it is applied or cannot split. Link: https://lore.kernel.org/20260908134739.96919-1-sj@kernel.org Fixes: 50585192bc2e ("mm/damon/schemes: skip already charged targets and regions") Signed-off-by: Liew Rui Yan Reviewed-by: SJ Park Signed-off-by: SJ Park Signed-off-by: Andrew Morton Cc: # v5.16.x (cherry picked from commit b3723b596b548c837a766aae3553c14a7b15af2b) Signed-off-by: SJ Park --- mm/damon/core.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 859a6a636ab0e..64ff03b15fdef 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -756,6 +756,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c, unsigned long sz = damon_sz_region(r); struct timespec64 begin, end; unsigned long sz_applied = 0; + bool skip = false; if (!s->wmarks.activated) continue; @@ -768,14 +769,11 @@ static void damon_do_apply_schemes(struct damon_ctx *c, if (quota->charge_target_from) { if (t != quota->charge_target_from) continue; - if (r == damon_last_region(t)) { - quota->charge_target_from = NULL; - quota->charge_addr_from = 0; - continue; - } if (quota->charge_addr_from && - r->ar.end <= quota->charge_addr_from) - continue; + r->ar.end <= quota->charge_addr_from) { + skip = true; + goto clean_charge_from_skip; + } if (quota->charge_addr_from && r->ar.start < quota->charge_addr_from) { @@ -783,17 +781,25 @@ static void damon_do_apply_schemes(struct damon_ctx *c, r->ar.start, DAMON_MIN_REGION); if (!sz) { if (damon_sz_region(r) <= - DAMON_MIN_REGION) - continue; + DAMON_MIN_REGION) { + skip = true; + goto clean_charge_from_skip; + } sz = DAMON_MIN_REGION; } damon_split_region_at(t, r, sz); r = damon_next_region(r); sz = damon_sz_region(r); + skip = false; } + } +clean_charge_from_skip: + if (r == damon_last_region(t)) { quota->charge_target_from = NULL; quota->charge_addr_from = 0; } + if (skip) + continue; if (!damos_valid_target(c, t, r, s)) continue; -- 2.47.3